The addition of enolate anions to carbonyl functions constitutes one of the most important and widely used synthetic techniques in organic chemistry. In particular the aldol condensation, which namely consists in the addition of an enolate anion to a carbonyl group of a ketone or an aldehyde followed by a protonation, is a well known reaction [see e.g.: H. O. House, Modern Synthetic Reactions, 2nd Edition, W. A. Benjamin Inc. (1972), p. 629 and following]. This aldol condensation is usually effected in the presence of a basic or an acidic catalyst and, starting from a ketone or an aldehyde, yields as an intermediate reactive species, an enolate and an enol, respectively.
The reaction is characterized by a series of complex equilibria which, depending upon the nature of the reactants and of the catalysts chosen, often lead to the formation of complex reaction mixtures. In most instances, aldol condensation is in fact accompanied by concomitant dehydrations, retrograde reactions (or retroaldolisations), and polymerisations, and consequently its industrial application suffers from serious drawbacks. In order to obviate to these disadvantages, several specific methods have been developed in the past; however, so far, none of them could be satisfactorily applied to the reaction occurring between 3,3-dimethyl-cyclohexanone and an aldehyde of formula EQU R--CHO (I)
wherein R represents a saturated, mono- or poly-unsaturated, linear or branced, substituted or unsubstituted univalent hydrocarbon or oxygen-substituted hydrocarbon radical.
The invention involves a novel process for producing substituted cyclic ketones, and it is therefore not important insofar as the process is concerned what "R" is, so long as the "R" constituent or group does not contain functional groups which will interfere with or prevent the reaction and that the CHO moiety remains functional. To date the applicant is unaware of any "R" constituent or group which cannot be used in the disclosed process.
Due to the interest presented by .alpha.-substituted cyclic ketone derivatives as intermediates for the preparation of certain perfume and flavour ingredients, as well as for the synthesis of certain carotenoids or related derivatives such as vitamin A or ionones, it is of primary importance to dispose of a synthetic procedure leading to a regioselective substitution in position .alpha. of an unsymmetrical ketone.